Homebrew PCBs

Adam Seychell wrote:
> Matthew Smith wrote:
>> Quoth Adam Seychell at 2008-06-05 18:23...
>>> They could be a different brand/formula photoresist. could you explain 
>>> what problems you had ? Is it negative or positive resist ?
>>> Was it a exposure, developing issue, or copper residue problem. The only 
>>> problem I've experienced with aged resists (>2 years) is a stubborn 
>>> residual invisible film left behind on the copper surface after 
>>> developing. It requires rigorous developing to remove it, and etching to 
>>> remove the rest.
>> Adam - I'll fire the same question back at you - with which brand did 
>> you have this specific problem - Kinsten?  If so, I'd be interested to 
>> hear as I've got a load of "mature" Kinsten stock that I'm about to use, 
>> having been out of the game for a couple of years.
>>
>>
> 
> I think the resist was Macdermid brand, negative active. I got a roll of 
> it several years ago and apply it myself. Because I develop the PCB 
> almost immediately after applying, I never have the residue problem. 
> Apparently the professionals never leave resist on any more than 24 
> hours or it becomes too difficult to develop.
> The only way around the problem is to develop about 2 or3 times longer. 
> If its really bad then the resist will get damaged due to excessive 
> developing before all the residue has had a change to be removed.
> 
> I develop in 1% NaCO3 30~40 deg.C as you do for all negative resists. I 
> I use a paint brush for the scrubbing.
> 
> The problem I found is the residue is invisible so it looks like the 
> developing is complete. But when you go to etch , the photoresist 
> residues are quickly revealed by un-etched copper areas.

Beware of swimming pool NaCO3 as it seems to be contaminated with something;)